Limitless Kv in relation to Drag racing

[Recovery Infraction]

I'm looking for an answer to something I've believed for some time.. That a high Kv is better for drag racing. I have 2350 as well as 2700kv motors that I use specifically for drag racing. 23-8s/27-6s. What is the importance of a higher kv in this application? REALLY? do I gear the 2700 lower because it spins higher and throw more gear at the 2300 just because it's a lower KV? Will someone PLEASE set me straight on this!? TIA??

 

[LibertyMKiii]

I have seen you can go much higher kv in drag because the motor is running for 4 seconds or less and typically takes the esc a little bit to know what is going on and cut power/amps.
With higher kv you have to gear waaay down.

One example I saw was Nic Case (long time ago) with a dragster/rail He ran 1.3 seconds somewhere around 96mph. This car had a 7000kv motor running 4s.
This would be similar to running 3500 on 8s.

 

[Recovery Infraction]

I have seen you can go much higher kv in drag because the motor is running for 4 seconds or less and typically takes the esc a little bit to know what is going on and cut power/amps.
With higher kv you have to gear waaay down.

One example I saw was Nic Case (long time ago) with a dragster/rail He ran 1.3 seconds somewhere around 96mph. This car had a 7000kv motor running 4s.
This would be similar to running 3500 on 8s.

Thank you, I still am trying to make the relationship between kv and drag though.. WHY a big kv? For instance, can that 7000 kv motor even START eating at 132'? Why is kv relevant to drag? I do appreciate your input though. ?

 

[LibertyMKiii]

Thank you, I still am trying to make the relationship between kv and drag though.. WHY a big kv? For instance, can that 7000 kv motor even START eating at 132'? Why is kv relevant to drag? I do appreciate your input though. ?

In the past drag classes were mostly 1 and 2 cell. They needed high KV to get the RPMs up.
It was also a goal of increasing total power in watts. Watts is an equation of volts x amps. The volts were limited by the 1s or 2s class so the only thing you could change would be the amp draw. Higher KV pulls more amps.

In your situation of 6s and 8s use, I suspect you have all the power and RPM needed. I honestly doubt you can go any faster on 8s versus 6s due to the limitations of traction.

Ideally you are just shooting for near 60k rpms knowing the car wont fully reach it. I am not sure what your voltage drop will be from the full 4.2v per cell, but I would estimate something close to these:

60,000 / 22v= 27xx kv
60,000 / 28v = 21xx kv

As I mentioned I don't have specific knowledge for drag racing with 6s or 8s so this is my best shot at it.

 

[Recovery Infraction]

In the past drag classes were mostly 1 and 2 cell. They needed high KV to get the RPMs up.
It was also a goal of increasing total power in watts. Watts is an equation of volts x amps. The volts were limited by the 1s or 2s class so the only thing you could change would be the amp draw. Higher KV pulls more amps.

In your situation of 6s and 8s use, I suspect you have all the power and RPM needed. I honestly doubt you can go any faster on 8s versus 6s due to the limitations of traction.

Ideally you are just shooting for near 60k rpms knowing the car wont fully reach it. I am not sure what your voltage drop will be from the full 4.2v per cell, but I would estimate something close to these:

60,000 / 22v= 27xx kv
60,000 / 28v = 21xx kv

As I mentioned I don't have specific knowledge for drag racing with 6s or 8s so this is my best shot at it.

That helps immensely! I was unaware that kv was directly related to amp draw. Thank you very much! And I must agree with you 8vs6. A good setup is what matters. Set up properly my 6s Mugen MGT 7 on 6s will Walk on my 8s limo I'm pretty sure..thanks again brother ??

 

[LibertyMKiii]

That helps immensely! I was unaware that kv was directly related to amp draw. Thank you very much! And I must agree with you 8vs6. A good setup is what matters. Set up properly my 6s Mugen MGT 7 on 6s will Walk on my 8s limo I'm pretty sure..thanks again brother ??

I know weight is a critical component. Definitely check the specs on batteries for their weight. I would be curious if a 4000 mAh pack has enough "juice" to get the job done and save a pound or 2.

Related to motor KV and amp draw. I tested a TP 4070 measures 40 x 107mm) it is a 2080kv D-wind motor. It pulled 6.5 Amps on the SkyRc tester and actually is a 2142KV motor. Another TP 4070 with the same 2080kv d-wind pulled around 3.6 amps, but was 2094kv . (no 2 motors are exactly the same)

I also Tested a TP4050 that is significantly smaller and for 3s and 4s use is a 3840kv, despite being smaller it was pulling over 8 amps due to the KV.

 

[Recovery Infraction]

I know weight is a critical component. Definitely check the specs on batteries for their weight. I would be curious if a 4000 mAh pack has enough "juice" to get the job done and save a pound or 2.

Related to motor KV and amp draw. I tested a TP 4070 measures 40 x 107mm) it is a 2080kv D-wind motor. It pulled 6.5 Amps on the SkyRc tester and actually is a 2142KV motor. Another TP 4070 with the same 2080kv d-wind pulled around 3.6 amps, but was 2094kv . (no 2 motors are exactly the same)

I also Tested a TP4050 that is significantly smaller and for 3s and 4s use is a 3840kv, despite being smaller it was pulling over 8 amps due to the KV.

View attachment 97892

Both my motors are TP. that's quite a significant drop from the mft.ratings. that being said I'm a little more comfortable with throwing 8 s at that 4070cm 2700 I have. 6s rated, but 8 for 2 second bursts? Sounds like this weekend should be experiment time!????

 

[LibertyMKiii]

Both my motors are TP. that's quite a significant drop from the mft.ratings. that being said I'm a little more comfortable with throwing 8 s at that 4070cm 2700 I have. 6s rated, but 8 for 2 second bursts? Sounds like this weekend should be experiment time!????

I know for speed runners with near 1:1 gearing the 2700 and 2900 TP Power motors tend to cook ESCs ?
BUT I would expect for short 2-3 second bursts in drag racing (with very reduced gearing) that would not be an issue. One local guy told me he prefers the Max5 for drag use, but I cannot see why an MMX8s wouldn't get the job done just as good and provide some data logs also. Gathering from data logs the voltage drop and RPMs would help a ton for making changes to gearing and batteries.

I'd imagine you don't need much gearing. Maybe setup to max around 90mph or less?

 

[Recovery Infraction]

I know for speed runners with near 1:1 gearing the 2700 and 2900 TP Power motors tend to cook ESCs ?
BUT I would expect for short 2-3 second bursts in drag racing (with very reduced gearing) that would not be an issue. One local guy told me he prefers the Max5 for drag use, but I cannot see why an MMX8s wouldn't get the job done just as good and provide some data logs also. Gathering from data logs the voltage drop and RPMs would help a ton for making changes to gearing and batteries.

I'd imagine you don't need much gearing. Maybe setup to max around 90mph or less?

I'm going to play around with the voltage and see what logs up. Great points.. gearing is shrouded in secrecy in drag so I doubt I'll get much help there other than trial and error. But that's what this is all about, and one of the reasons I love RC the way I do. For instance, if I hear someone say at the races, you can't run a 4070 2700 on 8. I can chime in with hell yeah you can!! Or, hell no you can't!!?

 

[LibertyMKiii]

I'm going to play around with the voltage and see what logs up. Great points.. gearing is shrouded in secrecy in drag so I doubt I'll get much help there other than trial and error. But that's what this is all about, and one of the reasons I love RC the way I do. For instance, if I hear someone say at the races, you can't run a 4070 2700 on 8. I can chime in with hell yeah you can!! Or, hell no you can't!!?

Good luck with it, I have been tempted to get into drag racing with a local group. I just cannot seem to pull myself away from the aerodynamics side of speed running.

 

[Recovery Infraction]

Good luck with it, I have been tempted to get into drag racing with a local group. I just cannot seem to pull myself away from the aerodynamics side of speed running.

I can appreciate speed runs. I haven't the vision nor the space to facilitate that. My initial setup was for speed and still have the entire limo GT aero situation going on, I just drag with it instead.

 

[GRC]

gorgeous paint job

 

[LibertyMKiii]

I can appreciate speed runs. I haven't the vision nor the space to facilitate that. My initial setup was for speed and still have the entire limo GT aero situation going on, I just drag with it instead. View attachment 97896

Wow that is amazing. I had not seen a dual element wing like that yet either.

 

[Recovery Infraction]

gorgeous paint job

Christopher John Sears did the paint. He's an artist for sure. But thank you!